Make sched_wakeup_task() globally visible

Previously, sched_wakeup_task() was limited to internal use within
the scheduler module.
This change makes it globally visible so that it can be reused
in semaphore.c for task wake-up operations.

Author: vicLin8712

include/sys/task.h

@@ -316,4 +316,7 @@ int32_t app_main(void);
  * Only one idle task exists per hart. Its priority is fixed to the
  * lowest level and its time slice is zero.
  */
-void idle_task_init(void);
+void idle_task_init(void);
+
+/* Wake up and enqueue task into ready queue */
+void sched_wakeup_task(tcb_t *);